As a last resort, perhaps the device can float to the surface and recharge using solar cells on the body. Considering the cost, serious consideration must be given as to how to avoid collisions with motorized vessels. I hope a solid program is also in place to ensure it doesn't attract unwanted attention from underwater predators - especially since it generates electrical fields.

I once caught a marlin in Mexico. When I read this story, I couldn't help but think of the possibility of someone snagging this thing--what a catch, and even a better fish story.
Yes, I know it will be used much deeper than would be accessible--but still the imagination wanders....